The present invention relates to an image reader capable of obtaining image data for an electrophotographic image forming apparatus, for example, and the image forming apparatus provided with the image reader.
A image reader (scanner) for obtaining image data for an image forming apparatus comprises a transparent document holder (document glass), illumination unit, CCD sensor, optical set, etc. The document glass is a substantially rectangular plate that serves to hold an object of reading, such as a sheetlike document, book, or cubic body. The illumination unit, which includes an illuminating lamp and a reflector, illuminates the object of reading set on the document glass. The CCD sensor receives reflected light from the object of reading that is illuminated with illumination light from the illumination unit, and converts an image contained in the object of reading into an electrical signal. The optical set includes a plurality of mirrors and reduced-scale lenses that are interposed between the document glass and the CCD sensor. An analog electrophotographic apparatus is designed so that an exposure mirror and a photoconductor drum are provided in place of the CCD sensor and that reflected light from the object of reading is guided directly to the drum. In this apparatus, a document glass (document holder), illumination unit, and optical set are arranged in like manner.
In the scanner (image reader) of this type, the illumination unit and a first mirror, which is located near the illumination unit and serves to reflect the reflected light from the object of reading in a given direction, are assembled together as a first carriage, which is movable along the document glass. Further, second and third mirrors, which serve successively to return the reflected light from the first mirror toward the CCD sensor, are arranged between the first mirror and the CCD sensor. They are assembled together as a second carriage, which is movable without changing its position relative to the first carriage.
The first and second carriages are moved so that the speed of the second carriage is half that of the first carriage, by means of a motor for generating driving force, a wire or belt for transmitting the driving force of the motor to the first and second carriages, and a reduction gear mechanism that reduces the rotational frequency of the motor as it adjusts the torque to a given value.
The reduction gear mechanism is composed of, for example, a motor pulley mounted on the shaft of the motor, a plurality of reduction pulleys arranged between the wire (or belt) and the motor pulley and capable of further reducing the driving force (rotational frequency) supplied to the motor pulley, and a plurality of timing belts or gear trains for transmitting the driving force between the reduction pulleys.
Thus, the image reader is a continuous physical system that includes a plurality of movable parts and movable components, such as the motor, wire or belt, first and second carriages, reduction gear mechanisms, etc. These parts and components have their respective natural frequencies that depend on their materials, shapes, methods of assembly, etc. It is known that they resonate to one another if their natural frequencies are equal.
If any oscillation is caused during the image reading operation of the image reader, then the quality of read image data will inevitably be lowered. For example, the image data quality may be lowered by a longitudinal-line fluctuation such that at least one of the carriages are staggered or moved in zigzags so that the CCD sensor inevitably reads image data as an image that oscillates in the advancing direction of the carriage.
At the time of shipment, the movable parts and components are assembled, adjusted, or shaped in an optimum state without resonation of the natural frequencies. Due to aging or prolonged use, however, the respective natural frequencies of the movable parts and components may change and undergo resonation.
If the quality of the read image data is lowered by resonance, it may possibly be improved by adjusting the tension on the wire or the torque of the drive motor. In most cases, however, the adjustment takes a lot of time. In many cases, moreover, the adjustment cannot improve the data quality. In these cases, it is necessary to recover and readjust the apparatus in the production line or plant or replace its defective parts or components.
An object of the present invention is to provide an image reader capable of maintaining high quality of read image data for a long period of time.
Another object of the invention is to provide an image reader designed so that an object of reading or a combination of an illumination mechanism and an optical set is moved and image information on the object is converted into an electrical signal, in which the quality of read image data cannot be lowered by oscillations of movable parts and movable components.
Still another object of the invention is to provide an image reader designed so that an object of reading or a combination of an illumination mechanism and an optical set is moved and image information on the object is converted into an electrical signal, in which resonation of the respective natural frequencies of movable parts and movable components can be reduced so that high-quality image data can be outputted, or an image forming apparatus including the image reader.
According to the present invention, there is provided an image reader comprising: a CCD sensor for converting image information into image data composed of electrical signals; a mirror set for transmitting image data on an object of reading to the CCD sensor; a movement mechanism for moving the mirror set and/or the object of reading at a given speed; a drive unit for applying driving force to the movement mechanism; and a driving force control mechanism adapted to change the value of drive current supplied to the drive unit when a peak of a fluctuation frequency detected by means of a fluctuation detector is equal to the natural frequency of the drive unit, the fluctuation detector being externally connectable and capable of processing an output signal from the CCD sensor and detecting the fluctuation frequency attained as the movement mechanism is moved and the peak of the fluctuation frequency.
According to the invention, moreover, there is provided an image reader comprising: a CCD sensor for converting image information into image data composed of electrical signals, a mirror set for transmitting image data on an object of reading to the CCD sensor; a movement mechanism capable of moving the mirror set and/or the object of reading at a given speed; a drive unit for generating driving force; a driving force transmission mechanism for transmitting the driving force generated by the drive unit to the movement mechanism; and a transmission condition changing mechanism for changing a condition for the transmission of the driving force generated by the drive unit when a peak of a fluctuation frequency detected by means of a fluctuation detector is equal to the natural frequency of the drive unit, the fluctuation detector being externally connectable and capable of processing an output signal from the CCD sensor and detecting the fluctuation frequency attained as the movement mechanism is moved and the peak of the fluctuation frequency.
According to the invention, furthermore, there is provided a method for detecting and restraining a fluctuation of an image of an image reader, comprising: transmitting image information on a straight-line image, extending in a first direction and having a length equal to the width of each pixel in a second direction perpendicular to the first direction, to a light receiving surface of a CCD sensor by means of a mirror set; moving the mirror set or the image in the first direction so that image data, continuous in the first direction and photoelectrically converted by means of the CCD sensor, is subjected to Fourier conversion; obtaining the frequency of a fluctuation of the image data obtained by the Fourier conversion and a maximum value of the amplitude thereof; comparing the frequency of the fluctuation with the natural frequency of a drive motor for generating driving force for moving the mirror set or the image in the case where the maximum value of the amplitude of the fluctuation is greater than a given value; increasing the level of current supplied to the drive motor in the case where the frequency of the fluctuation and the natural frequency are equal; and changing a condition for the transmission of the driving force from the drive motor to a mechanism for moving the mirror set or the image in the case where the frequency of the fluctuation and the natural frequency are not equal.
According to the invention, moreover, there is provided an image reader comprising: a transparent plate member for holding a test chart carrying thereon an image extending in a first direction and having a length equal to the width of each pixel in a second direction perpendicular to the first direction; an illuminating device capable of illuminating the test chart set on the plate member, thereby obtaining reflected light containing image information on the test chart; a CCD sensor for photoelectrically converting the reflected light and outputting image data corresponding to the image information; a mirror member for transmitting the reflected light toward the CCD sensor; a carriage member for moving the illuminating device and the mirror member along the transparent plate member; a motor for generating driving force; a driving force transmission member for transmitting the driving force generated by the motor to the carriage member; and an image data input-output section connected with a fluctuation detector externally connectable and capable of processing the image data delivered from the CCD sensor and detecting the fluctuation frequency attained as the carriage member is moved and the peak of the fluctuation frequency.
According to the invention, furthermore, there is provided a system capable of reducing fluctuation components of read image data attributable to oscillations of movable parts and movable components of an image reader having the movable parts and components and resonance of the whole image reader, comprising: a transparent plate member for holding an object of reading including a test chart; an illuminating device capable of illuminating the object of reading set on the plate member, thereby obtaining reflected light containing image information on the object of reading; a CCD sensor for photoelectrically converting the reflected light and outputting image data corresponding to the image information; a mirror set for transmitting the reflected light toward the CCD sensor; a carriage member for moving the illuminating device and the mirror set along the transparent plate member; a motor for generating driving force; a driving force transmission member for transmitting the driving force generated by the motor to the carriage member; and an image data input-output section connected with a fluctuation detector externally connectable and capable of processing the image data delivered from the CCD sensor and detecting the fluctuation frequency attained as the carriage member is moved and the peak of the fluctuation frequency, wherein the image information on the test chart is transmitted to a light receiving surface of the CCD sensor by means of the mirror set, the image data continuous in a first direction, outputted as the image information on the test chart is photoelectrically converted by means of the CCD sensor when the mirror set or the test chart is moved in the first direction, is subjected to Fourier conversion by means of the fluctuation detector connected by means of the image data input-output section, the frequency of a fluctuation of the image data obtained by the Fourier conversion and a maximum value of the amplitude thereof are obtained, the frequency of the fluctuation is compared with the natural frequency of the drive motor for generating the driving force for moving the mirror set or the image when the maximum value of the amplitude of the fluctuation obtained by means of the fluctuation detector is greater than a given value, the value of current supplied to the drive motor is increased when the fluctuation frequency and the natural frequency are equal, and a condition for the transmission of the driving force from the drive motor to a mechanism for moving the mirror set or the image is changed when the fluctuation frequency and the natural frequency are not equal, in the case where the object of reading is the test chart containing the image information on a straight-line image having a length equal to the width of each pixel in a second direction perpendicular to the first direction.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.